1. Field of the Invention
The invention relates to an inverter transformer, more particularly to an inverter transformer adapted to be connected to discharge lamps to form a lamp assembly that has uniform illumination among the lamps.
2. Description of the Related Art
A liquid crystal display (LCD) uses discharge lamps, such as cold cathode fluorescent lamps (CCFL), as a source of backlight illumination. The discharge lamps are driven by an inverter circuit, which usually includes an inverter transformer, in order to meet the requirement of high voltage outputs.
A conventional inverter transformer includes a core, a bobbin, and primary and secondary windings wound around the bobbin. The primary and secondary windings are adapted to be connected electrically and respectively to an electrical source and a load, which is the CCFL in this case.
As LCDs increase in physical size, the required length and number of CCFLs also increases, and the power required for driving the lamps increases accordingly.
In order to minimize production costs, the secondary winding is connected in the prior art to two CCFLs that are in parallel. Under ideal loading conditions, the CCFL exhibits negative thermal impedance characteristics, which can result in different actual impedances between individual lamps. Therefore, the current, and thus illumination, in individual lamps differ from each other during actual operation.
The CCFL comes in various configurations, such as L-shaped and U-shaped, depending on a particular application. The difference in illumination among individual lamps is more noticeable for the L-shaped and U-shaped lamps, and therefore, control over regulating the currents in the lamps is necessary. Although an impedance matching coil has been proposed heretofore to facilitate regulating the currents in the lamps that are connected to the same secondary winding, this regulating scheme not only increases production cost, but also takes up valuable space in circuit boards inside the LCDs.